Optical devices, such as laser diodes (LD) and light emitting diodes (LED) can be fabricated by crystal growth of a nitride-based group III-V compound semiconductor on a sapphire substrate, a SiC substrate, etc. As technical problems for optical devices of this type, there are improvements in heat dissipation performance and light extraction efficiency.
Recently, there has been proposed a technique in which a problem of heat dissipation performance can be solved and large current operation is feasible by bonding a nitride-based group III-V compound semiconductor to a substrate superior to a sapphire substrate or a SiC substrate in heat dissipation performance and peeling off the substrate by a laser lift-off method (see, U.S. Patent Application Publication No. US 2007/0298587.)
Concerning the improvement in light extraction efficiency as the other problem, it has been experimentally confirmed that optical output of two times or more is attained, compared to a flat light emitting surface, by processing an light emitting surface with strong alkali etching using a strong alkali solution such as potassium hydroxide or sodium hydroxide to make a rough surface.
The process of making the rough surface with the strong alkali etching has, however, a problem of difficulty in process integration because not only the light emitting surface of a light emitting device but also electrodes, a passivation film, a support substrate, etc. are eroded to some degree.